The invention relates to a method for producing a microsystem with pixels.
Thin layers made out of lead-zirconate-titanate (PZT) are widely used in the microsystem technology due to their advantageous physical properties, for example a high electromechanical coupling, a high dielectric constant or a high pyroelectric coefficient. A microsystem conventionally comprises a substrate as a carrier for the thin film, wherein the substrate comprises a membrane that is spanned by a silicon frame. It is known to deposit the lead-zirconate-titanate-thin layer on the substrate by a deposition method, in particular a sputtering process. A grid-like arrangement of pixels out of the thin layer is conventionally achieved by a photolithographic etching method. The pixels are electronically interconnected with electrodes that are, for example, made out of platinum or a chrome-nickel-alloy.
It is necessary that the membrane has a small thermal mass and a low thermal conductivity, so that thermal crosstalk between the pixels is low. This is achieved by the membrane being formed out of a poorly heat conducting material, for example silicon oxide, and being formed as thin as possible. The thickness of the membrane is typically 1 μm with a frame height of 400 μm. It is possible to structure the rear side of the substrate so strongly anisotropic that cavities can be formed using a deep reactive ion etching method. The cavities immediately extend to the membrane, so that the membrane is exposed on its side facing away from the pixels. It is desirable to make the membrane as thin as possible and with a sufficient high solidity, so that the pixels have a high functionality due to the low crosstalk.
In order to stabilize the membrane it is known to provide an additional Si3N4-layer on the substrate. However, the additional Si3N4-layer has the disadvantage that its heat conductivity is so high that the disadvantageous crosstalk between the single pixels is increased. Furthermore, producing the additional Si3N4-layer requires a further manufacturing step, whereby higher manufacturing costs are involved.